Variable of interface type ? what is the purpose of giving interface name as variable type?

Question

//SPDX-License-Identifier:MIT
pragma solidity ^0.8.6;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";

contract staking{
    IERC20 public s_stakingToken;
    IERC20 public s_rewardsToken;

     constructor(address stakingToken, address rewardsToken){
        s_stakingToken=IERC20(stakingToken);
        s_rewardsToken=IERC20(rewardsToken);
    }
}

can anyone explain the working of the above code snippet?

1. why interface name is given as a variable type? IERC20 public s_stakingToken;
2. how inside constructor, IERC20(stakingToken) will work?
3. Is IERC20() a constructor? as per my knowledge there is no constructor allowed in interfaces.

Answer 1

in simple terms 👇

No IERC20 is not a constructor.

In these code snippets, you are associating s_stakingToken with IERC20 functions.

When you assign the stakingToken to the IERC20 of s_stakingToken , you can access the IERC20 functions directly from s_stakingToken such as name, symbol, balanceOf, transfer.

So example, when you do s_stakingToken.name() it will return you the name of the ERC20 token located at the stakingToken address.